Gyromagnetic resonance method and apparatus



March 9, 1965 w. A. ANDERsoN ETAL 3,173,083

GYRMAGNETIC RESONANCE METHOD AND APPARATUS Filed Feb. 23, 1962 6Sheets-Sheet l March 9, 1965 w. A. ANDERSON ETAL 3,173,083

GYROMAGNETIC RESONANCE METHOD AND APPARATUS Filed Feb. 23, 1962 6Sheets-Sheet 2 March 9, 1965 W- A. ANDERSON ETAL GYROMAGNETIC RESONANCEMETHOD AND APPARATUS Filed Feb. 23, 1962 6 Sheets-Sheet 3 rea/w March 9,1965 W. A. ANDERSON ET AL GYROMAGNETIC RESONANCE METHOD AND APPARATUSFiled Feb. 25, 1962 6 Sheets-Sheet 4 @cora/'er March 9, 1965 W. A.ANDERSON ETAL GYROMAGNETIC RESONANCE METHOD AND APPARATUS Filed Feb. 23.1962 6 Sheets-Sheet 5 ffy d/Ef@ March 9, 1965 W. A. ANDERSON ETALGYROMAGNETIC RESONANCE METHOD AND APPARATUS Filed Feb. 23, 1962 6Sheets-Sheet 6 Waff@ orwef,

United States Patent() Aa,173,083 GYROMAGNETIC RESONAN CE METHD ANDAPPARATUS Weston A. AndersoiuFori-est A. Nelson, `and David L.

Wright, Palo Alto, Calif., assignorsV to .Varian Associates, Palo Alto,Calif., a corporationof `California Filed Feb. 23, 1962, Ser. No.174,950 signings. (Ci. 324-) This patent applicationis a`continuationain-part of patent application Serial No. 71,184 entitledGyromagnetic Resonance Method and Apparatus, tiled on November 23, 1960,by the same inventors, now abandoned in favor of this application.

This invention relatesin general to gyromagnetic resonanceapparatus andmore particularly to novel improved apparatus and methods utilizing sideband resonance techniques for `producing and detecting -gyro-rnagnetlcresonance.

The presentinvention involves the utilization, in gyromagneticresonancespectrometer systems, of a self-sustaining side band` resonanceoscillator to control the parameters ofthe measurement or analysischannels of the spectrometer systems to render them eld-frequency stabilized. The invention encompasses gyromagnetic resonance spectrometersystems of the side band resonance typetin whichthe parameters ofthemeasurement channel of the systems are so arranged that side bandresonances are `p roducedand, by suitable receiver circuitry, one ofthese side band resonance signals is observed, the spectometer employingtheself-.sustaining side band resonance oscillator toproducethemodulation signal necessary to produce `the side band resonance inthe spectrometer measurement channel. The presentinventionencompassesthe use of polarizing magneticlield modulation andtransmitter `modulation for producing the desired side band resonancesin the oscillator and measurement channels of the systems. Suchspectrometers are, because of their novel construction, held-frequencystabilized, insensitive to probe unbalance and are much improved overprevious systems with regard to zero drift.

`It is, therefore, the object of the present invention to provide novelimproved gyromagnetic resonance systems utilizingside band resonancetechniques.

Onefeature of the present invention is the provision ofnovelgyromagnetic Vresonance spectrometer systems which employ a measurementchannel controlled by a side band resonance oscillator channel, the`side band resonance being produced by either modulation of thepolarizing magnetic `field or modulation of the transmitter signal. i l

lAnother feature of the presentinvention is the provision ofnovel sideband resonance gyromagne-tic resonance spectrometer systems whichemploya side band resonance [measurement channel controlled by a side bandresonance oscillator channel, the side band resonances in the Vtwochannels being produced by either modulation of the polarizingmagneticjeld oi" modulation'of the transmitter signal. l

Another feature ofthe present invention is the provision of novelsystems of the above featured types wherein the side band oscillatorcontrols Vthe magnetic ieldstrength or radio frequency of themeasurement channel in accordance withithe oscillation frequency oftheoscillator.

` Still another feature of the present invention is the provision ofnovel systems of the above featured types wherein a-sweep throughtheresonance spectrum is produced by a sweep of the magnetic'eld of theoscillator ora-measurement channels or a sweep ofthe transmitterfrequency.

-These and other features and advantages of the present invention willbecome more apparent upon a perusal-0f Lce the following speciiiation`taken 1in `connection with the aompnyins drawgswhelen,

l'is :asblockrdiagramshowing a side band resonancevgyrornagneticvresonance spectrometer system employing "a Iside band" resonanceoscillator for jeld-frequency stability inwhich-self-'sustaininglaudio,modulation of the polarizing `magneticneldfisutilizzed to` produce Hthe side band resonancein Aboththefrneasnrernent arid Voscillator channels, the systernbeing asinglecoil type of resonance system,

FIG. 1A shows a modiiication ,made to the system ,of the type shown inFIG. Al for process contr-olapplications,

FIG. 2 is agraphical `illustration of the resonance signals obtained atcertain values of lield from a system of the type shown in FIG. l,

FIG. 3 is a'graph'ical illustration showing the frequency components'ofone of the side .band resonance signals of the type s hownin FIG. 2, l

FIG. 4 is a block diagram ofa side band resonance spectrometer systememploying a` Sideband resonance oscillator forlield-Lfrequencyhstability in which the transmitter section of the system ,is amplitudemodulated to produce fthefside band resonance condition while thereceiver sections ofthe measuring and oscillator channels are sensitivetoifrequency modulation for detecting `such resonance, the system beinga crossed-coils type of system,

FIG. 5 is a block diagram of a side band resonance type gyromagneticresonance spectrometer system employing a side band resonanceoscillator.forelddrequency stability in Which the transmitter section isfrequency modulated to produce a side band resonance andthe receiversections of the measuring and oscillator channels are sensitive toampiitude modulation for detecting the resonance conditioninthesidetband, the system being a single coil type of system,

FIG.. 6 is a block diagram of another type of gyromagnetic resonancespectrometer system utilizing a side band resonance oscillator forfield-frequency stability, i

FIG. 7 is a blockdiagram of a system incorporating the presentinventionwherein the samples `in the oscillator and the measuringchannelsihavediterent gyromagnetic ratios,

FIG. 8 is a block diagram of a spectometer system incorporating thepresent invention 4which also employs` a novel method and means forautomatically sweeping across a line in the spectrum tooptimize magneticeld adjustments,

FIG. 9 is a block diagram of a more conventional spectrometer `systemthan those ,shown above which also employs a gyromagnetic resonance sideband oscillator for control ofthemeasurement channel ofthe system,

FIG. l0 is a block diagram of a spectrometer system ot the presentinvention which is arranged to analyze a sample having adifferentgyromagnetic ratio than the oscillator sample,

FIG. l1 shows a block diagram of another embodiment of the presentinvetnion for use with samples having dilerent gyromagnetic ratios,

FIG. l2 illustrates apossiblemodiioation ofthe spectrometer system ofFIG. 1l, and

FIG. 13 is a block diagramof another embodiment of i the invention inwhich the oscillatorchann'el employs frequency modulation and thespectrometer channel employs magnetic lield modulation.

Referring now to FIG. lthere is shown in block diagram form a singlecoil forni of gyromagnetic resonance spectroscopy system embodying` thepresent invention.

The chemical sample 11 to be analyzed by means of gyromagneticresonance, for example, resonance of the nuclear magnetic momentsofuthe` sample, and the sample or substance 12 utilized in the sidenbandresonance' oscillator are placed in the strong unidirectional magneticfield H0 anw-3,088

in the gap of a permanent magnet or electromagnet represented by polepieces 13. An RI". coil 14 is located in close coupling relationship tothe sample 11 With its axis substantially perpendicular to theunidirectional magnetic field H0. A radio frequency transmitter 15, suchas a crystal controlled oscillator, is coupled to the coil 14 (throughan attenuator circuit 16, if desired) and supplies a radio frequencydriving field H1 to the sample 1l at an angular frequency w Ito producethe desired nuclear magnetic resonance in the sample 11 in a manner Wellknown in the art, side band resonance being produced in a mannerdescribed below. At or near resonance of the nuclear magnetic moments inthe sample l1 the coil 14 has induced therein a signal due to theresonance condition of the nuclei at the frequency w.

The unidirectional magnetic field H is modulated by an audio or lowfrequency (for example, 1 kc. to 1GO kc.) magnetic field Hm from theaudio or low frequency modulation coil 17 coupled to the nuclear sideband oscillator channel (to be Subsequently described) at an audio orlow frequency w1, the amplitude of the unidirectional magnetic field H0thus being modulated at the audio frequency rate to give a total fieldHZ=H0iHm cos (wlt-l-b).

To determine the effects of field modulation consider a special solutionof the phenomenological equations in the Physical Review article, vol.70, pages 460-74, 1946 by Felix Bloch. If we let mzMx-I-My, h=fy(HX+Hy)and wAq/HZ the equations may be written in the following form The fieldmodulation has the form HzzHo-l-Hm cos wlt which is equivalent towA=w0|yHm cos w11? where wozYHo and let Aw=w0-w. With the abovesubstitutions the differential Equation 3 has the solution t t' mFMIMOfexp ft rAmLaHm COS waffle/Ida' If the variation of Aw is sufficientlyslow, one obtains (4) ml-:ihlMoffleXpK-z'm) (tf-f) sin withsin wltHdtwith vHm

This equation may be integrated with the help of the identity exp{r sin@HQI JUG?) eXp (molt) i where Jn() are Bessel functions of the firstkind. Upon integrating one obtains Y resonances are obtained, eachresonance separated from the adjacent resonance by in magnetic fieldunits. These resonances are indicated diagrammatically in FIG. 2. Hereeach separate reso nance corresponds to a different value of n inEquation 5. lf we now select a given resonance signal, n, and Fourieranalyze the frequencies present in the signal, we find all frequenciesof the form w-l- (lc-n) w1 to be present where k is a positive ornegative integer. This is shown diagrammatically in FlG. 3 where thefrequencies present for the ,1:1 side band are represented; similarseparate frequencies exist for the other values of 11:0, 1, i2, etc. Inthe present illustration, the parameters of the system are selected suchthat the region represented by AH is slowly swept through to producethis n=1 side band IeSOYlZIlCC.

Thus, the total signal in the R.F. coil transmitted to the RF. amplifier18 includes a leakage signal at the transmitter frequency w which ismodulated by a nuclear resonance signal from the nuclear magneticmoments with a frequency component w as well as components at allfrequencies which differ from w by an amount w1, 2w1, 3w1, Thismodulated KF. signal is amplified by the radio frequency amplifier 1Sand fed to a diode ded tector circuit 19 which operates to demodulatethe signal and produce an output signal at the low or audio frequencyw1.

This w1 output is fed to an audio amplifier 21 for amplification andthen to an audio mixer or phase detector circuit 22 which obtains itsreference frequency w1 directly from the side band oscillator channelthrough a phase reference amplifier 22. The output of this mixer Z2contains a D.C. leakage free signal which is suitable for observation onan oscilloscope or for recording on a graphic recorder 23 or the like orfor integration in integrator 24 before recording. The unidirectionalmagnetic field H9 may be slowly swept through resonance as in a mannerutilized in previous gyromagnetic resonance spectrometers, for example,by a saw-tooth sweep generator 25 and sweep coil 26, the output of thesweep generator also being connected through switch 20 to synchronizethe recorder 23 when necessary. When it is desired to regulate thepolarizing field strength at one sample relative to the field strengthat the other sample, a small bias field may be supplied to one or theother of the samples, for eX- ample, by supplying an adjustable D.C.current through the sweep coil 26 from a control circuit in the powersupply.

Although the component w1 has been selected in the above example as theresonance signal component to be observed, it is obvious that, ifdesired, other components. of the resonance signal can be selected bythe use of the proper frequency selective circuits in the diodedetector..

lt should also be mentioned that the mode selection of; the resonancesignal, that is, dispersion mode or absorp. tion mode, may be made bymeans of controlling thephase of .the leakage voltage on the diodedetector 19 or into 22.

The side band oscillator utilized to provide theaudio or, low frequencymodulating signal to-they substance 11- cornprises the transmitterlcoupled (through an attenuator circuit 28, if desired) to the radiofrequency coil 2? surrounding the substance I2 to produce a drivingradio frequency field H1 at an angular frequency w at the substance. Thecoil 29' is coupled to the receiver and feedback section of the sideband oscillator includinga radio frequency amplifier 3l, diodedetector32, audio amplifier. 33, compensation circuit `itil andl fieldmodulation coil 35 which modulates the polarizing magnetic field H0 atthe substance 12 to produce'the desired side` band resonance signalfromthe substance; The sideband resonance signal from the substance 12andthe leakage signal from the transmitter 15 will be amplified inamplifier 3l and demodulated in the diode detector to produce an audioor low frequency signal output w1 which is amplified in the audioamplifier 33 and transmitted through the conipensation circuit to themodulation coil 3'. This side band oscillator is a 'self-excitedvoscillator in which the frequency ofthe audio or low frequency feedbacksignal varies with and is deterniined'by the strength of theunidirectional magnetic field Hu and the frequency w in accordance withthe general relationship wlz/'yHo-w Oscillationsat el are initiated in`the same manner as in feedback oscillators in general, i.e., noiseenergy at the proper frequencies initiates the oscillations which arefed back and build up until equilibrium isestablished. The range offield-frequency over which this system will opcrate is determined inpart by the audio or low frequency bandwidthof the amplifier 33 andmodulation coil 35; The output fromthe audio amplifier 33 may be coupleddirectly to the coils 17 and 3'5 without tlieneed` of passing throughany form of compensation circuit 34. However, to improve the exactreproducibility characteristics of the system on repeated runs of thespectrometer on the same sample, a compensation circuit 34 is desirableto hold the amplitude of theside band resonance signal substantiallyconstant over the audio or low frequency'band by compensating Vtheamplitude of the current being fed to the sweep'coil 35 as a function ofthe audio or low frequency or, in other words, to compensate for thelowering of the modulation index as the low frequency increases. Toobtain the desired increase in signal amplitude as the audio frequencyincreases and vice versa, .the compensation network may consist of aseries capacitor in the line between the amplifier 332 and the fieldmodulation coils 17, 35, Athe impedance of which decreases withfrequency iiicrease (see, for example, condenser 168 'in FIG, 10).' Inorder to prevent saturation of the sample and insure stability of thesystem, it may be desirable to include a limiter or automatic gaincontrol circuit in the compensa-V tion circuit. For` proper phase of thefeedback signal, a phase shifter circuit may be included in th'efeedback path if necessary, for example, in thecompensation circuitry.One` form of compensation circuitry is disclosed and claimed in UnitedStates patent application, Serial No.

131,414', entitled Gyromagnetic Resonance Apparatus,`

filed August 14, 1961,'by David E. Gielow andDavid L. Wright arid nowPatent No. 3,127,556 granted March 31, 1964; it is`a1so possible toprovide automatic gain control of amplifiers 31 and 18 and prevent gainvariations therein from affecting the detected` signalamplitude.

Side-band resonance oscillators are described and'` claimed in copendingpatent application Serial No. 1,91,-` 35 6, iiled April 30, 1962A in thename of Weston A. Anderf son, said application being acontinuation-in-part of Serial No;.57,793, filed September 22, 1960,4now abandoned, which was in` turn a continuation-impart of Serial No.767,654, filed @ctober 16, l958,lnow Patent- No. 3,147,428 issuedSeptember l, 1964.

Thisspectrometer also incorporates transmitter control in that the audiofrequency signal output. from the audio amplifier 33 is transmitted to.an audio discriminator circuit `37 as well as to the field modulatingcoils '1'7` and 35;

The audio discrminator' 37produces a D C. output signal having anamplitude proportional to the variation in the frequency oli from anormal value. This Variable am* plitude DC. signal isutilizedito operatea` control circuit such as a variable reactor 38 in the transmitter tovary the frequency -w in a niannerl-tocompensate Vfor drift of `the`field H0 or frequency we i ln-place` of .thedisc'riminator 37,aphasedetectorrcircuit and reference oscillatorV may be utilized(as-inFlG. 4).' It-isralsolobvious. to those skilled iii therart thatVthe-- error -signaloutput from the audio discriminator 37 could beutilized to control the H0 lield strength (asfin FIG. 4)' rather thanthe frequency ofthe Vradiofrequencyoscillator 1S for the same purpose;also, both the transmitter andthe H0 field. strength could be controlledsimultaneously.

This system is also provided with meanslrforconverting thenieasurementchannel into aside bandiresonance oscillator such thatinitialfadjustments may be conveniently made to the measurement channeland magnetic field parameters to provide optimum signal output from thespectrometer duringv subsequent sample investigation.` A

switch 34 isprovided so that the modulating coils may be switched fromthe output ofthe audio amplifier 33 to the output from-the audioamplifier 21. The measurement channel including the sample` 11 is thusconverted into a side-band-resonance oscillatorA and, by observing theamplitude of the audio signal output as by means of an audio orlowfrequency voltmeter 30,' the magnetic Vfield envelopirigl theV samplell may be adjusted and shimmed to obtain optimum*oscillatorfsignaloutput. After such system-optimizing, switchi34-l may be operated toreconnect the field modulating coils to the audio amplifier 33 solithat-an analysis maybe niade of the sample 11. This conversion-feature maybeutilized in the system to be subsequently described when appropriate.

lt will, of course-,be evident to those skilled inthis art thatsideband` resonance signals other than the one selected for illustrationpurposes, i.e., 11:1, may be utilized-iii carrying out the presentinvention. For example, the nt=-1 sideband resonance lends itself to theuse of the identical system described above provided the of 60Amegacycles, whichwas controlled over a narrow frequency range by theoutputdiscriininator 37, and the associated electromagnet 13 produced afield H0 of approximately\14,092 gauss. The bandpass` of the side bandresonance oscillator channel was suicient to permit the control channelto' lock in over a range of about 4 to 6 kc. Actually the fieldHo-frequency w relationship was set to give a nominal value ofmodulation frequency w1Y of 5 kc. This 4particular spectrometer systemwas tuned to operationV on the'uppersideband' (n=l). The sweep unit 25provided various sweep rates from 25"to 500 seconds with amplitudes ofl2 to 250 milligjauss. A well known sample spinner was utilized in` thespectrometer channel.

Referring to FIG. 1A there is shown certain apparatus which may besubstituted into. the spectrometer of FIG. l in order to adapt the sideband resonance spectrometer shown therein to a process control type ofinstrument. The sample under investigation, rather than being a singlesubstance placed within the radio` frequency coil 14, is a mixture madeupfoff substances 'represented `by arrows* A andB running through amixer valve 39 and then passing or flowing throughA thedielectric'conduit enclosed by the radio frequency coil-14. Thespectrometer operates in a manner described above and the signal outputfrom the Thetransmitteri 15 included a crystal integrator 24 istransmitted to a process control circuit 4G which automatically controlsthe mixing of the substances A and B in the mixer valve 39 in accordancewith the integrated signal obtained from the spectrometer circuitry. Inthis way a rapid analysis of the mixture is obtained and the signaloutput utilized to control the ratio of the substances in the mix in acontinuous manner.

rl`here are other methods of producing the side band resonances whichmay be used in place of the abovedescribed magnetic field modulatedsystem. In one such system, the transmitter signal is frequencymodulated While the receiver and feedback section of the system utilizesamplitude modulation detection (PMAM system). In another such system,the transmitter signal is amplitude modulated while the receiver andfeedback section of the system utilizes frequency modulation de teotionof the resonance signal (AM-FM system).

To obtain the results for AM-FM and FM-AM systems, one may considerseparately the RF. fields seen by the nuclei. For each different Fouriercomponent we may assume that the usual slow passage solution of thephenomenological equations is valid and then add the individualsolutions below. This method is perfectly valid so long as the separateside band spacings are large compared to the natural linewidths.

Referring now to FlG. 4, there is shown another embodiment of thepresent invention wherein both the side band resonance measurementchannel and the side band resonance oscillator channel employ amplitudemodulation of the radio frequency transmitter signal to produce themodulation of the oscillator substance and the substance being measuredfor obtaining the side band resonances desired. This system alsoutilizes the crossedcoil type of probe for both the oscillator andmeasurement channels although it will be understood by those skilled inthe art that the choice of single coil or crossed coil probes, or one ofeach type in the two channels, is a matter of individual preference.

The radio frequency signal w from the R.F. transmitter 41 is transmittedto an lamplitude modulator 42 which receives an audio modulating signalat frequency w1 from the audio amplifier 43 of the side band oscillatorto be subsequently described. The signal output from the amplitudemodulator 4Z to the RF. transmitter coil 44 (through attenuator 45, ifdesired) contains w, w-i-wl, and w-wl. The system parameters areselected such that resonance occurs in the sample 46 at one of the sideband frequencies, for example, w+w1. The signal into the probe is (1 -Msin alt) sin wt where Z..4=1ndex of modulation. The signal into the RF.amplifier 47 and limiter 48 from the receiver `coil 49 during upper sideband resonance is then given by gv cos wlt-leu sin wlt) and eu is the usignal and Ev is the v signal.

Under normal conditions ea,ev l thus 6 l, we expand 8 In passing the RF.signal through the limiter We fix and leave 0 unchanged. t

We now Fourier analyze 0. For M 1 this 1s simply 0=eu sin wlt-l-zI-evcos wit Thus with an audio phase detector one may select either the u orv mode signal.

Expressed in another way, if there is no resonance taking place in thesample, the output of the radio frequency amplifier 47 and limiter 43contains only w because the limiter removes all amplitude modulationfrom the w signal. If resonance is occurring, however, the signal intothe limiter contains both amplitude and frequency modulation of thecarrier w. The limiter removes the amplitude modulation and passes thefrequency modulation and, thus, the output of the limiter is a frequencymodulated carrier whose phase varies in accordance with the resonancesignal. The output from the RF. amplifier and limiter is passed to anRI". discriminator 51, the output of which is an audio signal atfrequency w1 which varies in amplitude with reso-nance. This output istransmitted through an audio amplifier 52 to an audio mixer circuit 53Where either the u or v mode component may be selected by the choice ofthe phase, by means of the phase shifter 54, of the audio referencevoltage from the audio amplifier 43 of the side band oscillator. TheD.C. output signal of this system is then transmitted to theoscilloscope 55 which receives its slow horizontal sweep signal from thesweep generator 56 which is utilized with sweep coil 57 to sweep throughthe spectrum.

In the side bland oscillator channel, the amplitude modulated signal istransmitted from the amplitude modulator 42 (through an attenuatorcircuit 58, if desired) to the transmitter coil 59.

As explained above, with resonance occurring in the oscillator substance61, the signal into the limiter 62 from the pick-up coil 63 and RF.amplifier 64 contains both amplitude and frequency modulation of thecarrier w. The limiter 62 removes the amplitude modulation and passesthe frequency modulation and, thus, the output of the limiter is afrequency modulated carrier whose phase varies in accordance with theresonance signal. The output from the limiter 62 is passed to an R.F.discriminator 65, the output of which is an audio signal at frequency w1which varies in amplitude with resonance. This output is transmittedthrough the audio amplifier 43 back to the amplitude modulator 42 tothereby provide a closed loop feedback circuit for sustainingoscillation of the system. The phase of the audio signal may be adjustedby the parameters of the audio amplifier 43, if desired. This systemgives both radio frequency and audio frequency gain with the advantageof not requiring large amplification at high frequencies. In addition,this system is not sensitive to changes in radio frequency gain.

The side band oscillator signal is also utilized for field control inthat the output from the audio amplifier 43 is transmitted through thebreak contacts of switch 60 to a discriminator 66 which produces a D.C.output signal as described above with regard to FIG. 1 to control theelectromagnet power supply 67. In lieu of the discriminator 66, an audiomixer 68 and reference audio oscillator 69 could be utilized by openingthe break contacts and closing the make contacts of switch 60. Thefrequency of transmitter 41 could be controlled rather than thepolarizing field or both could be controlled, if desired.

In FIG. 5, there is-shown a block diagram of another side band resonancegyromagnetic resonance spectrometer system employing a side bandoscillator. In this system the radio frequency driving signals for boththe oscillator and measurement channels are frequency modulated at theaudio rate and the sytsem employs a bridge type probe although thisfrequency modulation scheme is equally applicable to crossed-coilssystems and other single lcoil systems. The radio frequency transmitter71 generates a signal of frequency w which is coupled to a phasemodulator circuit 72 which is also coupled to the audio amplifier 73 ofthe side band resonance oscillator from which the phase modulatorreceives a modulating signal of frequency w1, the transmitter signalthus being frequency modulated at the audio frequency rate to give anoutput signal with components including w, w-l-wl, and w-wl. Thesesignals pass into an RF. limiter ciucuit 74 which serves to limit anyundesired amplitude variations occurring in the transmitter 71 ormodulator 72, since the receiver end of this system is sensitive toamplitude variations. Provided the transmitter 71 is stable so thatamplitude fluctuations do not occur and the modulator does not introduceany AM components, the limiter 74 may be omitted. The audio frequencyshould be large compared to the line spacings in a spectra and smallcompared to the bandpass of the RF. amplifier and limiter in thissystem. For example, an audio frequency of two kiloicycles may beselected as illustrative. The frequency modulated signal is transmittedto the bridge circuit 75' including the RF. coil 75 surrounding thesample being measured through a modulator circuit 75, for exampie, asingle side band modulator, which receives a sweep signal foradditionally modulating the signal to sweep through the spectrum at thefrequency rate of the variable frequency sweep oscillator 77. The singleside band modulation may also be placed in the modulation coil circuitin those systems utilizing polarizing field modulation such as in FIG. lif desired rather than the transmitter circuit. lt should also be notedthat in the above system the audio modulation held applied to the samplemay be swept in frequency to produce the desired spectrum sweep.

By phase modulating the transmitter signal, the RF. field of thetransmitter coil expressed in complex form is where is the maximumchange of phase angle produced by the modulator 72.

This system does not have the same restraint on the audio frequencyValue as does the system of FIG. l, wherein the magnetic field H isaudio modulated. As the audio frequency w1 used in the system of FlG. 1increases, higher Hm power is necessary since and this power demandlimits the audio frequency to lower values than can be readily utilizedin this frequency modulation system.

The values of the frequencies w and w1 and the strength of the field H0are so chosen that the nuclear resonance is made to occur in the sampleat one of the side bands, for example, 11:1.

In this case the magnetic field H0 must be equal to to produceresonance. The resonance signal in this case has only the frequencyw-l-wl. The RF. field at this frequency has an amplitude of 111.11m) andso the saturation parameter will be s=fy2H12]12(,e)T1T2. The input tothe RF. amplifier 7S thus comprises the: signal directly from thetransmitter circuit, including the frequency components o, w-l-wl, andw-wl, and, at resonance, the signal w-l-w1. The output of the RF.amplifier 7S is fed to an R.F. detector 7%. During the time no resonancesignals are stimulated, there will be no output from the RF. detector 79since the detector is only sensitive to the amplitude changes of the RF.voltage. However, in the presence of a resonance signal., an audiooutput at the frequency w1 will occur at the output of the RF. detector7.9V since the incoming wave will now have some amplitude modulation.The audio signal is amplified in audio amplifier 81 and is` convertedinto a DC. signal in the audio mixer S2. Either the u or v modecomponent may be selected by the choice of the phase, by means of phaseshifter 83, of the audio reference voltage from the audio amplier 73.The output from the audio mixer 82 is transmitted directly and alsothrough an integrator 84 to a dual channel recorder 85 which receivesits sweep drive from oscillator 77.

In the side band resonance oscillator system utilized in thisembodiment, the output of the modulator 72 is coupled through thelimiter 74 to the bridge circuit 80 including the RF. coil 86surrounding the oscillator substance in the magnetic field, theparameters of the radio frequency and magnetic field being chosen sothat resonance occurs in the sample at one of the side band frequencies.The resonance signal is transmitted through the radio frequencyamplifier 87 to the detector 8S, the output of which is coupled to theaudio amplifier 73 and through the feedback circuit to the frequencymodulator 72'. A discriminator S9 may also be used for control purposesas explained above.

Referring now to FIG. 6 there is shown another embodiment of the presentinvention including a side band resonance oscillator channel `comprisingradio frequency transmitter 91, attenuator circuit 92, the probeincluding transmitter coil 93, pick-up coil 94 and gyromagneticsubstance 9S, R.F. amplifier 96, RF. mixer 97, audio amplifier $8,compensation circuit 99, and eld modulator coil 101. The samplemeasurement channel com-` prises the transmitter 91, attenuator 102,transmitter coil 1&3, pick-up coil 101i, sample 165, R.F. amplifier 106,RF. mixer 1417', audio amplifier 1%, audio mixer 109, and an indicatingmeans such as, for example, an oscilloscope 110. It is noted that inthis embodiment the audio or low frequency modulation for side bandoperation is applied to both substances 95 and 165 by a singlemodulation coil 101 and this technique could also be employed in thesystem of FIG. l, if desired. In addition, the slow sweep signalutilized to sweep through the spectrum is applied from the sweep unit111 via sweep coil 112 to the side band oscillator channel of the systemas distinguished from the other sweep methods described above. Adiscriminator 113 .is utilized for magnet field control.

In all of the above systems, the gyromagnetic ratio of the oscillatorsubstance is the same as that of the sample under analysis, for example,both containing protons or both containing fluorine. In FlG. 7, there isshown an embodiment in which the two substances may be different, forexample, one proton and the other iiuorine. 1n this instance, afrequency synthesizer circuit 113 is utilized in association with asweep oscillator 114 and with a correction signal from the side bandoscillator output to produce a frequency signal synchronized with but ofa different frequency than the transmitter frequency. For example, thetransmitter signal may be approximately 60 megacycles for protons in theside band oscillator channel which includes the R.F. transmitter 115,RP. coil 116 surrounding the substance 117, RF. lamplifier 118, RF.detector 119, audio amplifier 120, compensation circuit 121, andmodulator coil 122. The output of the frequency synthesizer may beapproximately 56 megacycles for liuorine in the measurement `channelwhich includes the transmitter 115, frequency synthesizer circuit 113',RF. coil 123 surrounding the substance 124, RF. amplifier 125, RF.detector 12d and the phase detector 127 leading to the indicatingcircuits. In such a case, concentric samples may be employed includingsamples with similar atom portions separated by large chemical shifts.Also, a single mixed sample may be utilized for both the oscillator andmeasuring channels.

Referring to FIG. 8, there is shown a spectrometer system of the generaltype disclosed in the various above embodiments which also incorporatesa method of autom'atically sweeping across a line of the 'spectrometersample to permit optimizing lthe magnetic field adjustments beforemaking a sample run. A sweep circuit 128 including sweep coil 123' is`closed through switch 131' to provide a small, low frequency sweepsignal, for example, a signal with an amplitude comparable to alinewidth and a frequency of about 3 c.p.s., to the sample in themeasuring channel probe 129, the sweep signal also being transmitted asa reference signal to a phase detector 139 coupled to the output of theaudio amplifier and phase detector 129' of the measurement channel. Theoutput of the phase detector 131i is transmitted to a bias coil 132 tocontrol the strength of the polarizing iield H at probe #l relative tothe field at probe #2 to retain the line of the spectrum in the regionof the small sweep. The magnetic field may then be adjusted as byelectric current shims or magnet benders or the like until the highestvoltage reading is obtained on the D.C. voltmeter 130', the bias systemretaining the line centered during such field adjustments. The side bandoscillator in this system comprises the lradio frequency transmitter132', the oscillator probe 133 which includes the oscillator sample, theradio frequency amplifier 134, detector 135, the audio amplifier 13d,the compensation circuit 137, and the modulation coil 136 utilized tomodulate the field at both probes. The measurement channel includes theradio frequency transmitter 132', the measurement channel probe 129, theradio frequency amplifier 131, the detector circuit 139, the audio phasedetector 129' leading to the indicator circuitry 139', and the low oraudio frequency sweep circuit 14). In this embodiment, the bias coil 132also doubles as the spectrometer sweep coil.

Referring now to FIG. 9, there is shown a spectrometer system of a moreconventional type utilizing a side band oscillator for controlling thetransmitter in accordance with the oscillator output. The side bandoscillator channel of this system includes the transmitter circuit 141coupled to the radio frequency coil 142 surrounding the oscillatorsample 143 through an attenuator circuit 144, pickup coil 144', theradio frequency amplifier 145, an RJ?. phase detector 146, an audioamplifier 147, the field modulator circuit 148 and the field modulationcoil 149 coupled to the oscillator substance 143. The measurementchannel of this system includes the transmitter 141, attenuator 151, theradio frequency coil 152 surrounding the sample 153, pick-up coil 153',the radio frequency amplifier 154, RF. phase detector 155, and theindicating system including the recorder 159 and integrator 160. A sweepof the resonance signal is provided by the sweep circuit 162 andmagnetic field sweep coil 163. A discriminator 164 is coupled to theoutput of the audio amplifier and is utilized to control the frequencyof the transmitter by means of, for example, a variable reactor tothereby stabilize the system. Rather than controlling the transmitter,of course, it is possible to control the strength of the magnetic fieldsuch as shown in FIG. 4.

The system shown in FIG. l0 is designed for utilization when the nucleiof the control sample are different than the nuclei of the spectrometerchannel, for example, protons and iiuorine, respectively. Separatetransmitters 161 and 162 at the proper Larmor frequencies, for example,approximately 60 mc. for the protons and 56 mc. for the fiuorine, areutilized in the two channels. The control channel includes theattenuator 163, RP. coil 164, R.F. amplifier 165, diode detector 166,audio amplifier 167, compensation condenser 168, and modulation coil 169for modulating the H0 field at both samples. The spectrometer channelincludes the attenuator 17d, crossed R.F. coils 171, RF. amplifier 172,diode detector 173, audio amplifier 174, audio phase detector 175 andassociated phase reference amplifier 176, and indicators 177.

Qperation of this system is very similar to operation of the systemshown in FIG. l and described above. In the present system, however, theslow sweep generator 178 feeds two sweep coils 179 and 180 which serveto sweep the field HD at both samples. The coils are arranged such thatthe field is swept in opposite directions at the two samples, inpush-pull fashion, to thereby give an increased sweep rate. Thediscriminator 131 provides an error signal which is fed to the variablereactor circuits 182 and 183 associated with the two channeltransmitters 161 and 162, respectively, to control the frequencyoutputs. The attenuat-or 134 is provided when desired to compensate forthe fact that frequency changes will be different for the two channels.

Referring to FIG. 11, another form of system suitable for use wtihsamples having different gyromagnetic ratios is shown. This system issomewhat similar to the system of FIG. lO and like elements bear likereference numerals primed. Rather than controlling the transmitters 161'and 162', the output signal from the discriminator 181', is utilized tocontrol the field at the spectrometer channel sample by means ofcompensation coil 185. In lieu of the compensation coil 185 or inaddition thereto, a magnetic field iiux stabilizer 136 could be utilizedto control the magnetic field. Such a iiux stabilizer is shown in U.S.Patent 2,930,966, issued March 9, 1960 to W. Bell and M. Packard. Thediscriminator output may be coupled to the galvanometer coil 137 of thefiux stabilizer, the output of the stabilizer being coupled to theassociated field coil 188. In lieu of the discriminator 181' forcontrolling the compensation coil 135 and/ or iiux stabilizer 186, aphase lock system comprising audio mixer 139 and associated oscillator19@ could be employed by opening the break contacts of switch 189 andclosing the make contacts thereof. The transmitters in this applicationmust be highly stable.

FIG. l2 illustrates a modification that may be made in FIG. ll toconvert it to a system using a common R.F. transmitter 161'. Only thetransmitter end of the system is shown. rl`he RF. signal for thespectrometer channel is obtained from a radio frequency oscillator 191and multiplier 192. The output of the RF. oscillator 191 is alsotransmitted to a second multiplier 193 and thence to a mixer 194 Wherethe multiplier signal is beat with the radio frequency from thetransmitter 161 to give a difference frequency. This differencefrequency is transmitted through a filter and amplifier 195 to a mixer196 which receives a reference signal from an audio oscillator 197. Theoutput from the mixer 196 is a DC. signal which passes through a filter198 to a variable reactor to control the frequency of the radiofrequency oscillator 191. Assume that the frequency to attenuator 176 isto be 55 mc. and that to attenuator 163' is 60.1 mc. The R.F. oscillator191 may be 5 mc. which is multiplied ll times by multiplier 192 to 55mc. Multiplier #2 increases the signal to the mixer 194 l2 times to 60mc. The output of mixer 194 is .l mc. and it is mixed in mixer 196 witha .l mc. signal from oscillator 197. The RF. oscillator frequency isthus automatically controlled to maintain the proper relationshipbetween the two driving radio frequencies.

The system shown in FIG. 13 illustrates the fact that the one channel,for example, the control channel, may employ frequency modulation whilethe other channel, for example, the spectrometer channel, may employmagnetic field modulation, or vice versa. This system is very similar tothe system shown in FIG. 5 and like elements bear like referencenumerals primed. The difference lies in the fact that the output of thelimiter 74 is not utilized as the driving radio frequency for thespectrometer channel. Rather, the transmitter output, with sweepmodulation, is used as the spectrometer driving RF. signal and the lowfrequency modulation of the spectrometer channel is produced by themagnetic field modulation coil 199 coupled to the output of the audioamplifier 73'. It is, of

sirenas ltainedinthe above description or. shown inthe accompanyingdrawings shall be interpreted as illustrative and not in "a limitingsense.

What is claimed is:

1. Gyromagnetic resonance apparatus including `a meas- =urement channeland an `oscillator channel, said Ineas- A-urement channeladapted toIcontain-afirst gyromagnetic substance `and said oscillator channel`adapted to contain-a-tsecond gyroimagnetic substance-means forproducing a, unidirectionalr magnetic field forpolarizing said.subst-arises, means for applying driving radio frequency magneticfields to said A. substances atan `angle to said polarizing magneticfield to` produce gyromagnetic resonance in said substances, means for`modulating one of said polarizing or radiofrequencymagnetic fieldsapplied to each of said two substances lat -aperiodic low frequency rateto produce radio frequency side bandV reso- ;nance signals from thesubstances, the. parameters of the polarizing and radiofrequency ,fieldsat each substance .beingso `selectedgthat resonance at one of the sideband frequencies ispro-duced in each substance, means` in saidmeasurement channel fondetectingathe resonance condition rin said firstsubstance, said oscillator channel rincluding circuit meansforfsupply-ing the low frequency fmodulation signal to.said polarizingor radio frequency magnetic `elds,"said low frequency ,modulationproducin-g the sideband resonancefsignals from the substances,

saidcircuit means including means for vdetecting said `side bandresonancesignal insaid second substance to produce .an output signal` atsaid lowfrequency ratefor use by said circuit :means as said lowfrequency modula- =substances to thereby sweep through `thercsonance insaid t measurement channelsubstance.

`3. Gyromagnetic'resonance apparatus `as `claimed in claim l wherein`said meansl for modulating onev of said 'fields at i each substancecomprises =means for. modulating fsaid" polarizing magnetic 'fieldatsaid ylow frequency rate.

`4; Gyromagnetic resonance apparatus as claimed in .claim 3 `includingmeans for sweeping one of said radio frequencyor` polarizing magnetic`fields at one-of said substances Ato therebysweep through theresonancein said measurement channel substance.

5..Gyromagnetic'resonance apparatus'as 'claimed in claim Sawherein saidmeans formodulatingsaid ipolarizing magnetic field includes at least onemodulation coil coupled i-toasaid` oscillatorchannel circuit means andpositioned in saidpolarizing `magnetic field.

6. Gyromagnetic reso-nance apparatus as claimedin claiml wherein'saidmeans Ifor'modulating one of' said fields `at each @substance comprisesVmeans lfor modulating said` radio. lfrequency magnetic fields.

7. .Gyromagnetic' resonance apparatus as claimed. in claim 6 includingmeans for sweeping one of said radio frequency.. orpolarizing magnetic`fields at one .ofsaid substances` to thereby lsweep throughtheresonancein said measurement channel substance.

8. Gyromagnetic resonance apparatus as claimed in claim 6 wherein saidmeans for modulating said radio frequency magnetic fields includesamplitude modulator means in said radio frequency field applying means.

9. Gyromagnetic resonance apparatus as claimed in claim 6 wherein saidImeans for modulating said radio frequency fields includes frequencymodulator means in said radio frequency field applying means.

.14 l0. Gyromagnetic resonaneeapparatus as .claimedin claim 1 includingmeans responsiveto said .oscillator channel output signal forcontrolling at least one ofsaid polarizing or radiofrequency.magneticiieldsapplied to said measurement. channel` substance.

11. Gyromagnetic resonance.iapparatus asclaimed in claim 1T()whereinsaid. means responsive tosaidoscillator channel .output signalcontrols the strength ofsaid polariz- `ingtmagnetic field.

12. .Gyromagnetic resonance apparatus as claimed `in claim .10 whereinsaid means. responsive tosaid oscillator channel output signal, controlsY'the`freque`ncyof said radio frequency. 'magnetic field.

`13. Gyromagnetic resonance apparatus as claimed n.in

claim `10 whereinxsaid `last meansdnchidesmea'ns 4for convertingfrequency changes -`in F'said lowfifrequeny .out-

`put signal. into control signalamplitude. changes Iforause incontrolling saidfields.

14. Gyromagne'tic. resonance. apparatusas claimed-in `claim'10.inclu`ding means for sweeping one of said radio frequency or'polarizing .magneticfields at one ofisaid substances to thereby sweepthrough the resonance in said measurement channel substance.

l5. Gyromagnetic resonance. apparatus fas claimed'in .claim 1 havingmeans'for at times converting said `measurementchannel into fanoscillator channel comprising means insaid detecting means in saidfirstchannel fordetecting the side band resonance s ignaLinsaidffirstsubstance to produce an output signal atsaid'low frequencyrate, `and means for at times coupling saidfsideband signal detectingmeans tosaid rneansfor modulating one of said polarizing or radiofrequency magneticffieldsap- 'plied'to said first substance so astofprovidesaid'low frequency modulation signal to,produce"`theradiofrequency side band resonance signals"-from said"firs't substance.

16. Gyromagnetic resonance Happaratus including a ,measurement jchannelandA anl 'oscillator channel, 'said measurement channel radapted "tocontain a `first `gyromagnetic .substance and said oscilla-tor channeladapted Lto contain a Ysecond gyrornagnetic substance; means for theparameters of thepolarizing and radio 'frequency fields at eachsubstance being so selected "thatesonance at one of thesideibandfrequencies is, produced lin-.each substance, means in said`measurement .channeliifor 'detecting'wthe resonance conditionin`sa'idiirst substance,

said` oscillator channelincludingcircuit meanslfor supplying the lowfrequencymodulation signal to saiclp'olarizingmagneticfiel`saidtlow@frequency modulatiompro- 'ducing thesi-de band resonancesignals from the sulbstances, saidcircuitmeans includingmeansfor'detectoingsaid sideban'dresonance signal insaid secondsuib- `stancetoproduce an output signal'atsai'd low 'frequency -rate `for use by saidcircuitmeans as-'said low frequency modulation signal, .andmeansresponsive to said.os`cil lator channel output` signalforcontrolling. atleast'one of said polarizing orradiotfrequency:magneticffields applied to said measurementchannelsubstance.

17. Gyromagnetic resonance lapparatusas Vclaimed in claim 16..whereinsaid means responsive tosaid oscillator channel output signal controlsthe strength of said polarizing magnetic field.

18. Gyromagnetic resonance apparatus as claimed in claim 16 wherein saidmeans responsive to `said oscillator channel output signal controls thefrequency of said radio frequency magnetic field.

19. Gyromagnetic resonance apparatus as claimed in claim 16 includingmeans for sweeping said polarizing magnetic field at one of saidsubstances to thereby sweep through the resonance in said measurementchannel substance.

20. Gyromagnetic resonance apparatus including a measurement channel andan oscillator channel, said measurement channel adapted to contain afirst gyromagnetic substance having one gyromagnetic ratio and saidoscillator channel adapted to contain a second gyromagnetic substancehaving a gyromagnetic ratio different than said first substance, meansfor producing a unidirectional magnetic field for polarizing saidsubstances, means for applying driving radio frequency magnetic fieldsto said substances at their respective Larmor frequencies and at anangle to said polarizing magnetic field to produce gyromagneticresonance in said substances, means for modulating one of saidpolarizing or radio frequency magnetic fields applied to each of saidtwo substances at a periodic low frequency rate to produce radiofrequency side band resonance signals from the substances, theparameters of the rpolarizing and radio frequency fields at eachsubstance being so selected that resonance at one of the side bandfrequencies is produced in each substance, means in said measurementchannel for detecting the resonance condition in said first substance,said oscillator channel including circuit means for supplying the loWfrequency modulation signal to said polarizing or radio frequencymagnetic fields, said low frequency modulation producing the side bandresonance signals from the substances, said circuit means includingmeans for detecting said side band resonance signal in said secondsubstance to produce an output signal at said low frequency rate for useby said circuit means as said low frequency modulation signal,

211. Gyromagnetic resonance apparatus as claimed in claim 2() whereinsaid means for modulating one of said fields comprises means formodulating said polarizing magnetic field at said low frequency rate.

22. The method of stabilizing a gyromagnetic resonance apparatus havinga measurement channel and an oscillator channel, said measurementchannel including a first gyromagnetic substance and said oscillatorchannel including a second gyromagnetic substance, including the stepsof producing a unidirectional magnetic field for polarizing saidsubstances, applying driving radio frequency magnetic fields to saidsubstances at an angle to said polarizing magnetic field to producegyromagnetic resonance in said substances, modulating one of said p0-larizing or radio frequency magnetic fields applied to said twosubstances at a low frequency rate to produce radio frequency side bandresonance signals from the substances, the parameters of the polarizingand radio frequency fields being so selected that resonance at one ofthe side band frequencies is produced, detecting the resonance conditionin said first substance, and detecting the resonance condition in saidsecond substance and producing an output signal at said low frequencyrate therefrom, :said low frequency output signal being utilized as the.modulating signal for modulating said one field.

23. The method as claimed in claim 22 wherein said 'step of modulatingone of said fields comprises modulating said polarizing magnetic fieldat said low frequency zrate.

'24. The method as claimed in claim 22 wherein said 'step of modulatingone of said fields comprises modulating said radio frequency magneticfield.

25. The method as claimed in claim 24 wherein said Step o f :modulatingvsaid radio frequency magnetic field 1.6 comprises amplitude modulatingsaid radio frequency field.

26. The method as claimed in claim 24 wherein said step of modulatingsaid radio frequency field comprises frequency modulating said radiofrequency field,

27. The method as claimed in claim 22 including the step of controllingat least one of said polarizing or radio frequency magnetic fieldsapplied to said measurement channel substance in response to changes insaid oscillator channel output signal.

28. 'The method as claimed in claim 27 wherein said last step comprisescontrolling the strength of said polarizing magnetic neld.

29. The method as claimed in claim 27 wherein said last step comprisescontrolling the frequency of said radio frequency magnetic field,

30. The method as claimed in claim 22 comprising the step of at timesconverting said measurement channel into an oscillator channel bydetecting the side band resonance signal in said first substance toproduce an output signal at said low frequency rate, and modulating oneof said polarizing or radio frequency magnetic fields applied to saidfirst substance with said output signal to produce the radio frequencyside band resonance signals from said first substance.

31. Gyromagnetic resonance apparatus including a measurement channel andan Oscillator channel, said measurement channel adapted to contain afirst gyromagnetic substance and said oscillator channel adapted tocontain a second gyromagnetic substance, means for producing aunidirectional magnetic eld for polarizing said substances, means forapplying driving radio frequency magnetic fields to said substances atan angle to said polarizing magnetic field to produce gyromagneticresonance in said substances, means in said measurement channel fordetecting the resonance condition in said first substance, means formodulating one of said radio frequency or polarizing magnetic fieldsapplied to said oscillator channel substance at a low frequency rate toproduce a radio frequency side band resonance signal from saidsubstance, the parameters of the polarizing and radio frequency field atsaid oscillator channel substance being so selected that resonance atone of the side band frequencies is produced, said oscillator channelincluding circuit means for supplying the low frequency modulationsignal to said radio frequency or polarizing magnetic field at saidoscillator channel substance, said low frequency modulation producingthe side band resonance signals from the substance, said circuit meansincluding means for detecting said side band resonance signal in saidoscillator channel substance to produce an output signal at said lowfrequency rate for use as said low frequency modulation signal, andmeans responsive to said oscillator channel output signal forcontrolling at least one of said polarizing or radio frequency magneticfields applied to said measurement channel substance.

References Cited in the file of this patent UNITED STATES PATENTSAnderson Apr. 9, 1963 OTHER REFERENCES

1. GYROMAGNETIC RESONANCE APPARATUS INCLUDING A MEASUREMENT CHANNEL ANDAN OSCILLATOR CHANNEL, SAID MEANSUREMENT CHANNEL ADAPTED TO CONTAIN AFIRST GYROMAGNETIC SUBSTANCE AND SAID OSCILLATOR CHANNEL ADAPTED TOCONTAIN A SECOND GYROMAGNETIC SUBSTANCE, MEANS FOR PRODUCING AUNDERICTIONAL MAGNETIC FIELD FOR POLARIZING SAID SUBSTANCES, MEANS FORAPPLYING DRIVING RADIO FREQUENCY MAGNETIC FIELDS TO SAID SUBSTANCES ATAN ANGLE TO SAID POLARIZING MAGNETIC FIELD TO PRODUCE GYROMAGNETICRESONANCE IN SAID SUBSTANCES, MEANS FOR MODULATING ONE OF SAIDPOLARIZING OR RADIO FREQUENCY MAGNETIC FIELDS APPLIED TO EACH OF SAIDTWO SUBSTANCES AT A PERIODIC LOW FREQUENCY RATE TO PRODUCE RADIOFREQUENCY SIDE BAND RESONANCE SIGNALS FROM THE SUBSTANCES, THEPARAMETERS OF THE POLARIZING AND RADIO FREQUENCY FIELDS AT EACHSUBSTANCE BEING SO SELECTED THAT RESONANCE AT ONE OF THE SIDE BAND